Truck needed new shocks, so I brought it to "my Guy", told him to give it a once over and lube the front end, he asks, need an oil change? I was due in a few hundred miles, so I said, yeah go ahead, synthetic he asks, I say nah, just dino please. So I now have an unknown 15w40 circulating through my Duramax, unknown filter and I'm not the least bit curious or concerned.. The wife's Rav 4 just popped the message that it's time for maintenance , so we rode the factory fill for just about 5,000 miles. Dealer is going to do it, using Toyota synthetic whatever. I've lost "the oil fever" I guess. hmmmmmm, didn't think I'd see the day !!!!!